double fault 
noun Tennis
An instance of two consecutive faults in serving, counting as a point against the server.The Frenchman serves two consecutive double faults before sending an attempted lob clear of the baseline....
- She admitted to being a little rusty, which showed in several double faults and foot faults.
- The British No 2, now up to No 98 in the rankings, was not disturbed by 12 double faults in the match.
verb
(double-fault) [no object] Serve a double fault: she double-faulted on the final point...
- Rafter started the brighter and broke serve when Agassi double-faulted, holding out to take the first set.
- But Enqvist stormed back to tie it, only to double-fault on his last serve before Agassi hit a backhand cross-court winner to end the first set.
- Last year, when she double-faulted at break point in the Wimbledon final against her sister, there were dark rumours that it had been decreed as Serena's year.